Parcel sorters are machines used in material handling to convey and direct packages to different destinations. Most sorters are limited in speed, therefore the maximum sortation rate (number of packages that a sorter can process per unit of time) for a given mix of package sizes is limited. Given this speed limitation, in order to maximize the rate of certain sorters, including sorters able to parallel process more than one incoming stream of packages, it is necessary to reduce the gaps between packages to the minimum. This is particularly true for sorters known as “sliding shoe” sorters and narrow-belt crossbelt sorters in which a semi-continuous stream of packages can be induced. One such sliding shoe sorter is described in Veit, et al. U.S. Pat. No. 6,866,136, the contents of which are incorporated by reference herein. A number of systems for controlling the gaps between articles being fed to induction systems for sorters are known, including Zeitler, U.S. Pat. No. 6,629,593, Doane, et al. U.S. Pat. No. 5,038,911.
An induction system is the name given to the equipment used to prepare the flow of packages that is fed into a sorter. This preparation sometimes includes singulating and aligning the incoming packages and then adjusting the gaps between the packages. Except for systems which dynamically track previously identified packages, part of the induction equipment consists of means of identification of the destination of each package. This can be done by the use of laser scanners or cameras able to read bar codes or other types of printed labels on each package. There are other available means of package identification like, for example, RFID tags, but this invention applies to systems that rely on line of sight to read labels or printed surfaces in order to identify packages by optical means (laser scanners or cameras), not by radio frequency. In some markets, like CEP (courier, express and parcel) for example, the package identification label(s) can be located anywhere on the surface of a package being conveyed, and not on a particular face as it is done in other applications. If all identification labels are located on the top (or bottom) of the packages being conveyed, scanning (reading destination labels by a laser scanner or camera) can be done from above or below only. The problem is to read the package identification label(s) which can be located on other surfaces of the packages (front face, back face and sides).